FIG. 4 is a drawing illustrating a configuration of a related-art battery pack. The battery pack includes a lithium-ion battery 1, a fuel gauge IC 2, and a protection IC 3. The battery pack also includes power supply terminals 5 and 6 and a communication terminal 7 that are connected to a battery-powered device such as a cell phone or a digital camera.
The fuel gauge IC 2 includes a CPU 2A and may also include other components such as a memory and a communication circuit. The fuel gauge IC 2 detects charge and discharge currents of the lithium-ion battery 1, calculates a remaining battery level (or a remaining energy level) of the lithium-ion battery 1 by digitizing and totaling the detected charge and discharge currents, and sends the calculated remaining battery level via the communication circuit to the battery-powered device such as a cell phone or a digital camera.
The protection IC 3 turns off a switch 4 provided in a charge/discharge path and thereby stops charging or discharging of the lithium-ion battery 1 if overcharge or overdischarge of the lithium-ion battery 1 is detected. The protection IC 3 also generates status data indicating the overcharge or the overdischarge while the switch 4 is turned off and supplies the status data together with an interrupt signal to the fuel gauge IC 2.
Meanwhile, patent document 1 discloses a data processing unit that operates in multiple control modes including a measurement mode for measuring the remaining battery level of a battery. In the measurement mode, the current level supplied from the battery is minimized to save power.
[Patent document 1] Japanese Laid-Open Patent Publication No. 2005-12960